Four years ago, I had a problem with the right taillight on my E39. All of its functions—directionals, brakes, parking, reverse—failed. I assumed that it had to be due to a bad ground. I was right. I remember it being incredibly difficult to pull the connector out of its socket, and when I did, I discovered that the ground pin had snapped off inside the plug. I was able to remove it, but since it had broken off from the connector on the taillight, it seemed to be ruined. I bought a used $60 taillight on eBay and installed it.
The problem back in 2022.
Last month, the problem came back. I was alerted to it when I signaled with my right directional and heard it clicking twice as fast as normal. This is the audio feedback of what is usually due to a bad bulb. Then I noticed that in the little display in the instrument cluster, it said that a brake light was out, likely indicating that the whole-taillight problem had returned. Because I had some more-than-around-the-block driving coming up, and because I take it upon myself to fight the stereotype that BMW drivers are a**holes who don’t ever signal, I wanted to fix it ASAP.
I tried to unplug the connector, and found it was seized. Yup, deja vu all over again.
We meet again, Mister, uh, Bond. That’s a pun worthy of Dohn Roush.
Prying the connector with two small screwdrivers, I broke away plastic until I got to the solid rectangular sections where I could lever it off from the socket. When the two sections were apart, I could see what a corroded mess everything was. The ground pin was broken again, but this time I wasn’t able to pull it out from the plug.
Same failure, different year.
It seemed that this time I needed not only the taillight assembly, but a pigtail for the connector that I’d need to splice on as well. A search on eBay looked like it would set me back about $100 for the pair. I was about to pull the trigger on it when I wondered whether I could do an old-fashioned hack and simply wire a new ground.
I remembered from the last time that I’d pulled the thing apart that the prongs in the socket are extensions of the flat metal that makes up the base plate of the taillight assembly, and thus can’t be separately replaced like pins in many connectors. That was why I replaced the whole unit. But this time, I wondered if I could just attach a ground wire directly to the plate itself. The problem is that it’s not just one plate—each light has its own ground connection. I imagined needing to solder ground wires onto each. Then I futzed around with a multimeter and found where the ground path gets shared. It seemed that if I connected a single ground wire there, it would solve the problem.
The back of the taillight assembly. The circled area shows where the ground path is shared with other lights.
I was about to solder a ground wire onto that plate when I realized there was an even easier solution: I could use a piggyback spade connector, one of those little do-dads where you slide its female end onto a male spade terminal (they’re actually called “quick-connect terminals,” but so many people call them spades that I give up), and it gives you two males.
The piggy-back spade in my hand about to be attached to the plate at the terminal at the arrow.
I crimped a female spade onto a foot-long length of black wire, slid it and one of the ground wires onto the piggyback, slid the piggyback onto the shared ground terminal on the plate, crimped a ring connector onto the other end of the new black ground wire, and connected it to a convenient chassis ground. Then I took some electrical contact cleaner, plugged and unplugged the connector and socket a few dozen times to clean off the corrosion, wiped everything down, and tested it. It worked perfectly.
As I buttoned everything up, I saw what the root of the problem was: The taillight failed in exactly the same way it did four years ago because the drainage path for water running off the trunk hasn’t changed. It runs down the gutter and over the plastic lip of the taillight assembly. There’s a foam seal inside it, but apparently it’s not doing the trick.
Pretty obvious once you look at it.
The part number for the foam seal is 63216911696 for the right taillight, 63216911695 for the left. The right one is coming up as NLA on GetBMWParts, but isolated vendors still appear to have them. I’ll piggyback it onto an order the next time I need something.
But the right taillight is working, and with it, its directional. And that’s important. Because, after all, the last thing I want to be is some a**hole in a BMW :^)
—Rob Siegel
Rob’s most recent book, The Best of The Hack Mechanic, is available here on Amazon, as are his seven other books. Signed copies can be ordered directly from Rob here.
